The right atrium.
Blood flow goes:
vena cava > right atrium > tricuspid valve > right ventricle > pulmonary artery > pulmonary vein > left atria > mitral valve > left ventricle > systemic circulation
Veins from the lung
Well.... first you need to identify what is chamber 3.
There are four chambers. Left atrium, Right atrium, Left ventricle and Right ventricle.
Right atria.
The vena cavas. Either the superior vena cava, which is at the top of the heart, or the inferior vena cava which is at the bottom. The blood goes into the right atrium, then to the right ventricle, and so on and so forth.
As all artery's (apart from the pulmonary) carry oxygenated blood and the vena cava does not, i would say that the vena cava is a vien
Inferior vena cava
The inferior vena cava brings blood back to the heart from the lungs.
the right atrium through the superior and inferior vena cava
The caudal vena cava returns blood to the heart. It return deoxygenated blood
Inferior vena cava and superior vena cava.
The superior vena cava.
the inferior vena cava caries de-oxygenated blood.
right atrium
The vena cavae, which returns blood from the bottom half of your body back to your heart.